For driving auxiliary machines mounted on the turbojet engine, such as electric generators or oil or fuel pumps, which are required for operation of the turbojet engine or of the aircraft on which it is mounted, the required power is generally drawn from the main shaft. A twin-spool turbojet engine comprises two coaxial shafts: one, a low-pressure or LP shaft, connecting the low-pressure compressor to the low-pressure turbine, together forming the LP spool; the other, a high-pressure or HP shaft, connecting the high-pressure compressor to the high-pressure turbine, together forming the HP spool. In the case of such an engine, the power is generally transmitted to the auxiliaries by a radial arm, accommodated in an arm of the intermediate casing, one end of which comprises a conical pinion which interacts with a pinion rigidly connected to the high-pressure spool. The other end is mechanically connected to a box comprising a plurality of gears and forming a support for the auxiliary machines while also driving them. When the engine is a turbofan engine, the radial transmission shaft or driveshaft passes through the two streams, primary flow and secondary flow, because the gearbox for driving the accessories, also referred to as the AGB (Accessory Gear Box), is mounted on the casing of the fan generating the secondary flow.
A known driveshaft is formed of two elements known as the primary shaft and the secondary shaft. The first shaft element or primary shaft is connected at one of its ends to a means for providing mechanical transmission to an engine shaft of the turbojet engine. The second shaft element or secondary shaft is connected at one of its ends to a means for providing mechanical transmission to the gearbox for driving the accessories. An intermediate bearing for supporting the driveshaft can be provided in a portion of the radial arm. An intermediate bearing of this type generally comprises a plurality of rolling bearings for supporting the driveshaft when it is rotating.
In operation, the radial arm of the intermediate casing is subjected to aerodynamic forces. The deformations caused by these aerodynamic forces on the radial arm result in a first misalignment of the driveshaft in the region of the connection between the first shaft element and the second shaft element and a second misalignment of the driveshaft in the region of the intermediate bearing. These misalignments thus appear in different zones and produce an unbalance and vibrations of the driveshaft in the radial arm, resulting in particular in a moment in the region of the rolling bearings of the intermediate bearing, which reduces the driving efficiency of the shaft.